The conventional diesel engine is driven while the phase difference between the phase of a camshaft, which is the drive source of fuel injection of a fuel injection pump and determines timing of fuel injection, and the phase of a crankshaft of the engine is kept at a certain value.
By changing the phase difference forward or rearward following the state of the engine, the engine can be driven efficiently.
As a device changing phase of the camshaft of the fuel injection pump, there is well known a hydraulic timer unit. An example thereof is shown in below patent literature 1.
The hydraulic timer unit comprises a timer piston (it is also referred to as “shuttle piston”) between a camshaft coupling fixed to the camshaft of the fuel injection pump and a pump driving gear to which rotation of the crankshaft is transmitted so as to change the phase angle of the shafts.
The timer piston spline-fits the outer peripheral surface of the camshaft coupling straightly, and a pump driving gear spline-fits the outer peripheral surface of the timer piston helically.
According to this construction, the phase difference between the camshaft coupling and the pump driving gear can be changed by sliding the timer piston along the spline direction of the camshaft coupling.
This slide of the timer piston is performed by oil pressure, and the oil pressure is controlled by an Engine Control Module (ECM) which controls the engine.
Accordingly, the ECM controls the timer piston to the advanced side or the retarded side following the state of the engine so as to make the timing of fuel injection pertinent.
Now, with regard to such a fuel injection system that is described above, an engine stopping process is performed for example that an operator performs a stopping operation with an operation part such as a key switch, and then the ECM stops fuel injection to the engine so as to stop the engine.
Conventionally, in this stopping process, the timer piston is stopped at a position at which the piston exists at the time that the operator performs the stopping operation or a position at which the piston exists at the time that fuel injection is stopped.
Namely, the timer piston remains at the position of normal driving of the engine.
The timer piston is generally controlled hydraulically, whereby the timer piston cannot be controlled at the time of starting the engine.
Accordingly, at the time of starting the engine, the timer piston still exists at the position at which the piston exists at the time that the stopping process is performed (that is, the above-mentioned position of normal driving of the engine).
However, it is generally known that the more the timing of fuel injection is advanced, the more the start ability of an engine is improved.
Accordingly, with regard to the conventional fuel injection system, the start ability at the time of starting the engine is not necessarily good, whereby actuation time of a starting motor is long so that the load applied on a battery is large.
There is conventionally known a fuel injection system which controls drivingly a fuel injection pump injecting fuel to a cylinder of a diesel engine, a hydraulic timer unit changing the phase of timing of fuel injection, a governor adjusting fuel injection amount, and the like.
An example of such a conventional fuel injection system is described in the patent literature 1.
With regard to such a fuel injection system, for example, position of a rack provided within a governor is generally controlled drivingly following engine rotation speed or manifold pressure of a supercharger (turbocharger). The relation thereof has been memorized previously in an ECM which is an example of a control means of the engine and the fuel injection system, and an example of the relation is shown in FIG. 6.
With regard to a graph in FIG. 6, the axis of abscissas shows “engine rotation speed” and “manifold pressure” of the supercharger and the axis of ordinates shows “rack position”. The graph shows curves as described below.
With regard to the relation between manifold pressure of the supercharger and rack position, an intake rack position limit curve RT shows the relation between manifold pressure and rack position at which the fuel injection amount is maximized. So to speak, the curve is an upper limit line of the rack position.
With regard to the relation between engine rotation speed and rack position, a rotation speed rack position limit curve RM shows the relation between engine rotation speed and rack position at which the fuel injection amount is maximized. So to speak, the curve is an upper limit line of rack position.
With regard to the relation between engine rotation speed and rack position, a rotation speed rack position minimum curve RS shows the relation between engine rotation speed and rack position at which the fuel injection amount is minimized. So to speak, the curve is a lower limit line of rack position.
Though the intake rack position limit curve RT does not depend directly on engine rotation speed, the intake rack position limit curve RT and the rotation speed rack position limit curve RM may have the same rack position RC (point EC). Accordingly, based on the point EC, the intake rack position limit curve RT and the rotation speed rack position limit curve RM can be shown in one graph.
Namely, the intake rack position limit curve RT can be drawn as if the curve RT changes depending on engine rotation speed.
In addition, FIG. 6 shows an example of a fuel injection system of a ship or the like.
Now, conventionally, the ECM selects one of the intake rack position limit curve RT and the rotation speed rack position limit curve RM as the upper limit line of rack position as described below.
The ECM selects one of the lines, which makes the control range of rack position narrower, as the upper limit line.
For example, in the case that the engine idles and rotation speed is low, that is, in the case that engine rotation speed is M1 and manifold pressure is F1, the intake rack position limit curve RT, which makes the control range of rack position narrower than the rotation speed rack position limit curve RM, is selected as the upper limit line.
By this selection, the maximum fuel injection amount can be limited so as to suppress discharge of unburnt gas and black smoke.
Therefore, at the actual operation, the ECM selects the intake rack position limit curve RT as the upper limit line in the case that the engine rotation speed is between M1 and MC for example. On the other hand, the ECM selects the rotation speed rack position limit curve RM as the upper limit line in the case that the engine rotation speed is between MC and M2.
Namely, a curve passing through a point ET1, a point EC and a point EM2 is the upper limit line of rack position.
With regard to the above-mentioned fuel injection system, in the case that fuel injection amount is adjusted based on engine rotation speed, for example, maximum fuel injection amount and minimum fuel injection amount corresponding to engine rotation speed have been determined previously, and fuel injection amount is adjusted within this range. Namely, in this case, the relation between engine rotation speed and the maximum fuel injection amount and the relation between engine rotation speed and the minimum fuel injection amount have been memorized previously in the control means such as the ECM of the fuel injection system, and fuel injection amount is controlled based on these relations.
Now, in the case that engine rotation speed is lower than the predetermined minimum set rotation speed for improving engine failure-proof ability or another reason, there is a fuel injection system like the above mentioned controlling fuel injection amount to be increased following a decrease of the engine rotation speed. Namely, in the case that the engine rotation speed is the minimum set rotation speed, such as the case of idling, when load is applied on the engine by engaging a clutch or the like, the engine rotation speed may become lower than the minimum set rotation speed so as to cause engine failure. However, by increasing fuel injection amount following the fall of engine rotation speed at the lower rotation side than the minimum set rotation speed, the engine failure is prevented.
With regard to such a fuel injection system, the relation between engine rotation speed and fuel injection amount for increasing the fuel injection amount following the fall of the engine rotation speed at the lower rotation side than the minimum set rotation speed has been memorized in the control means corresponding to the certain predetermined minimum set rotation speed as mentioned above. Accordingly, when the minimum set rotation speed is changed, below defects may be caused.
The minimum set rotation speed is the minimum rotation speed of the range adjustable by operating a throttle or the like and is the engine rotation speed at the time of idling normally. Accordingly, for example in the case that the minimum set rotation speed is increased, when load is applied on the engine by engaging a clutch or the like at the time of idling, operability and driving feeling may be spoiled. The increase of fuel injection amount following the fall of engine rotation speed at the lower rotation side than the minimum set rotation speed is based on the relation between engine rotation speed and fuel injection amount determined corresponding to the certain minimum set rotation speed. Accordingly, in the case that the minimum set rotation speed is increased, the amount of fall of the engine rotation speed caused by applying the load may be increased and the fall of the engine rotation speed caused by applying the load may be not enough to increase fuel injection amount sufficiently. When such a phenomenon occurs, the recovery of fall of engine rotation speed by applying the load requires a measure of time, thereby spoiling operability and driving feeling.
To the contrary, in the case that the minimum set rotation speed is decreased, unnecessary fuel may be injected excessively so as to increase discharge of unburnt fuel.
Patent Literature 1: the Japanese Patent Laid Open Gazette 2004-218636